Modem agriculture, including silviculture, often requires the planting of large numbers of substantially identical plants genetically tailored to grow optimally in a particular locale or to possess certain other desirable traits. Production of new plants by sexual reproduction can be slow and is often subject to genetic recombinational events resulting in variable traits in its progeny. As a result, asexual propagation has been shown for some species to yield large numbers of genetically identical embryos, each having the capacity to develop into a normal plant. Such embryos must usually be further cultured under laboratory conditions until they reach an autotrophic “seedling” state characterized by an ability to produce their own food via photosynthesis, resist desiccation, produce roots able to penetrate soil and fend off soil microorganisms.
Some researchers have experimented with the production of artificial seeds, known as manufactured seeds, in which individual plant somatic or zygotic embryos are encapsulated in a seed coat, such as those disclosed in U.S. Pat. No. 5,701,699, issued to Carlson et al., the disclosure of which is hereby expressly incorporated by reference.
Typical manufactured seeds include a seed coat, a synthetic gametophyte and a plant embryo. Typically, the seed coat is a capsule having a closed end and an open end. The synthetic gametophyte is placed within the seed coat, such that the gametophyte substantially fills the seed coat. A cotyledon restraint may be centrally located within the synthetic gametophyte. The cotyledon restraint includes a centrally located cavity extending partially through the length of the cotyledon restraint and sized to receive the plant embryo therein. The well-known plant embryo is approximately 4–7 millimeters in length and roughly 0.5 millimeters in diameter. The shape of the plant embryo is somewhat cylindrical, but is irregular in cross-section and varies in diameter along its length. The plant embryo includes a radicle end and a cotyledon end. The plant embryo is deposited within the cavity of the cotyledon restraint cotyledon end first. The plant embryo is typically sealed within the seed coat by at least one end seal.
In the past, delivery of the plant embryo within the seed coat has utilized vacuum pick-up devices to transfer the plant embryo through the manufactured seed production line. In such transfer systems that utilize vacuum pick-up devices, the plant embryos one at a time are grasped at their sides from a first position and transferred to a second position, for example, by an automated robotic arm. Attached to the end of the robotic arm is a pick-up head to which a source of vacuum is connected. The pick-up head includes a tip having a tip opening designed to grasp and hold a single plant embryo via vacuum pressure. After the pick-up head grasps the embryo, the embryo is subsequently transferred to the second position, which may be for placing the embryo into the seed coat, placing the embryo on a temporary carrier, or releasing the embryo onto a different surface in a desired location or orientation. The surface may be a temporary storage location, or a movable surface, such as a conveyor belt, movable web, or positioning table, to name a few. Once the robotic arm has transferred the pick-up device to the second position, the source of vacuum is shut off to release the embryo.
Although such plant embryo delivery systems utilizing vacuum pick-up heads are effective at transporting plant embryos, they are not without their problems. For example, a problem may exist when the vacuum pick-up head attempts to release the embryo into the seed coat or other desired locations. Specifically, in applications where the embryos are kept moist or wet (i.e.; hydrated embryos) to prevent damage from desiccation, the embryo may remain attached to the pick-up head during cessation of vacuum pressure due to the surface tension formed between the moisture on the embryo and the contact area of the pick-up head tip. In this case, to release the embryo from the vacuum pick-up head, a puff of air pressure is expelled out of the vacuum head tip opening to overcome the surface tension and to force the embryo out of the vacuum head. In some instances, the burst of air flow is either insufficient to release the embryo or too great, in which case, the embryo may be damaged by the impact force of the embryo against the bottom of the restraint. In either case, viable embryos may be wasted, which is costly in commercial applications. Further, the effects of surface tension and the conventional methods for overcoming the same may cause unwanted movement of the embryo, which in turn, affects the orientation of the embryo for insertion into the seed coat, and may lead to improper placement of or damage to the embryo.